The present invention relates to a circuit arrangement comprising a phototransistor whose emitter-base path is bridged by a resistor.
Such a circuit arrangement has been described, for example, in the periodical "Siemens Components", 20 (1982), No. 3pages 83-84, FIG. 2, incorporated herein by reference. The bridging of the base-emitter path of the phototransistor has the purpose of carrying off the collector-base inverse current that flows in the unilluminated condition of the phototransistor. An increase of the inverse voltage strength of the phototransistor by about a factor of 2 when compared to a phototransistor having an open base terminal is thus achieved. The resistor, however, is also effective in the illuminated condition of the phototransistor and deteriorates its current gain.